Goodwill and Other Intangible Assets - Balances of Goodwill by Reporting Unit (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Goodwill [Line Items]
Gross book value		$ 450.5
Accumulated impairment charges		(40.6)
Goodwill, beginning balance	$ 409.9
Foreign exchange and other adjustments	0.1
Goodwill, ending balance	410.0
Capital Markets - Software Solutions
Goodwill [Line Items]
Gross book value		103.7
Accumulated impairment charges		0.0
Goodwill, beginning balance	103.7
Foreign exchange and other adjustments	0.0
Goodwill, ending balance	103.7
Capital Markets - Compliance and Communications Management
Goodwill [Line Items]
Gross book value		253.0
Accumulated impairment charges		0.0
Goodwill, beginning balance	253.0
Foreign exchange and other adjustments	0.1
Goodwill, ending balance	253.1
Investment Companies - Software Solutions
Goodwill [Line Items]
Gross book value		53.2
Accumulated impairment charges		0.0
Goodwill, beginning balance	53.2
Foreign exchange and other adjustments	0.0
Goodwill, ending balance	53.2
Investment Companies - Compliance and Communications Management
Goodwill [Line Items]
Gross book value		40.6
Accumulated impairment charges		$ (40.6)
Goodwill, beginning balance	0.0
Foreign exchange and other adjustments	0.0
Goodwill, ending balance	$ 0.0